The use of one or more stages of pivoting guide vanes in a turbomachine having an annular gas flow, or the like, is well known in the gas turbine engine and compressor art. Such guide vane stages comprise a plurality of individual vanes distributed circumferentially about the annular gas stream and pivoting in unison under the influence of a mechanical linkage.
One particular arrangement utilizes a plurality of small vane gears each secured to a central vane spindle oriented spanwisely with respect to a corresponding individual vane, with each vane gear meshing with an annular ring gear for establishing synchronized collective motion of the vane stage. An example of this general type of arrangement may be seen in the disclosure of U.S. Pat. No. 4,439,104 issued to Edmonds. The ring gear of the Edmonds disclosure is supported by an external housing of the compressor portion of the turbomachine, with individual gears secured to a spindle section of each vane for collectively and simultaneously positioning each of the Edmonds' inlet guide vanes.
The positioning of the ring gear, and hence the collective positioning of the entire vane stage, is accomplished in the prior art by coupling one of the vane gears to a rotary actuator, with that particular gear then functioning as a drive pinion for driving the ring gear and thus the remaining vane gears. While effective, such a system includes a number of inherent disadvantages, foremost of which is the premature wearing of the driving pinion gear which transmits the entire actuator force to the ring gear. Such premature wear can result in increased mechanical backlash between the pinion gear and the remaining driven gears, and in the extreme case such backlash may in fact diminish overall turbomachine performance by leaving a mismatch between the desired and actual orientation of the vane stage.
Another disadvantage of the prior art pinion gear system is the localized premature wear on the ring gear support bearing which must accommodate a locally high radial force in the vicinity of the pinion gear. Such localized wearing not only shortens the service life of the ring gear support bearing, but can exacerbate the localized gear tooth wear and backlash problem.
What is required is a vane actuation system which avoids undesirable localized wear of one or more of the vane gears and the synchronizing ring gear.